1. Field of the Invention
The present invention relates to a switching power source apparatus based on a quasi-resonance control method, and particularly, to a switching power source apparatus capable of improving power conversion efficiency and reducing switching noise.
2. Description of the Related Art
The quasi-resonance control method is one of methods for controlling a switching power source apparatus having a switching element. During an OFF period of the switching element, a voltage of free oscillation occurring at a drain of the switching element drops. When the voltage drop reaches a bottom level, the quasi-resonance control method detects it and turns on the switching element so as to reduce a switching loss and noise. The method is disclosed in, for example, Japanese Patent Publication No. 08-289543.
A switching power source apparatus proposed in the above-mentioned patent publication has a primary circuit connected to a primary winding of a transformer, a secondary circuit connected to a secondary winding of the transformer, and a controller connected to a tertiary winding of the transformer. The controller detects a bottom voltage of free oscillation after a flyback period and controls a switching element accordingly.